2. Universidad Cardenal Herrera-CEU

Bacteriophages are types of viruses that infect bacteria. They are the most abundant and diverse entities in the biosphere, and influence the evolution of most bacterial species by promoting gene transfer, sometimes in unexpected ways. Although pac-type phages can randomly package and transfer bacterial DNA by a process called generalized transduction, some mobile genetic elements have developed elegant and sophisticated strategies to hijack the phage DNA-packaging machinery for their own transfer. Moreover, phage-like particles (gene transfer agents) have also evolved, that can package random pieces of the producing cell's genome. The purpose of this review is to give an overview of some of the various ways by which phages and phage-like particles can transfer bacterial genes, driving bacterial evolution and promoting the emergence of novel pathogens.

Bacteriophage-mediated horizontal gene transfer is one of the primary driving forces of bacterial evolution. The pac-type phages are generally thought to facilitate most of the phage-mediated gene transfer between closely related bacteria, including that of mobile genetic elements-encoded virulence genes. In this study, we report that staphylococcal cos-type phages transferred the Staphylococcus aureus pathogenicity island SaPIbov5 to non-aureus staphylococcal species and also to different genera. Our results describe the first intra- and intergeneric transfer of a pathogenicity island by a cos phage, and highlight a gene transfer mechanism that may have important implications for pathogen evolution.

Genetic transduction is a major evolutionary force that underlies bacterial adaptation.Here we report that the temperate bacteriophages ofStaphylococcusaureusengage in adistinct form of transduction we term lateral transduction. Staphylococcal prophagesdo not follow the previously described excision-replication-packaging pathway but insteadexcise late in their lytic program. Here, DNA packaging initiates in situ from integratedprophages, and large metameric spans including several hundred kilobases of theS.aureusgenome are packaged in phage heads at very high frequency. In situ replication beforeDNA packaging creates multiple prophage genomes so that lateral-transducing particles formduring normal phage maturation, transforming parts of theS.aureuschromosome intohypermobile regions of gene transfer.

Arbitrium-coding phages use peptides to communicate and coordinate the decision between lysis and lysogeny. However, the mechanism by which these phages establish lysogeny remains unknown. Here, focusing on the SPbeta phage family’s model phages phi3T and SPβ, we report that a six-gene operon called the “SPbeta phages repressor operon” (sro) expresses not one but two master repressors, SroE and SroF, the latter of which folds like a classical phage integrase. To promote lysogeny, these repressors bind to multiple sites in the phage genome. SroD serves as an auxiliary repressor that, with SroEF, forms the repression module necessary for lysogeny establishment and maintenance. Additionally, the proteins SroABC within the operon are proposed to constitute the transducer module, connecting the arbitrium communication system to the activity of the repression module. Overall, this research sheds light on the intricate and specialized repression system employed by arbitrium SPβ-like phages in making lysis-lysogeny decisions.